Reducing glare for objects viewed through transparent surfaces

Abstract

In a method of detecting objects behind substantially transparent surfaces, a polarimeter with pixelated polarizer array architecture records raw image data of a surface and obtains polarized images. Glare is reduced in the polarized images to form enhanced contrast images. The glare reduction method selects optimal pixels from a subset of a super pixels of polarizing filters and displays the optimal pixels.

What is claimed is: 
     
         1 . A method of detecting objects behind substantially transparent surfaces, the method comprising:
 recording raw image data of the surface using a polarimeter with pixelated polarizer array architecture and obtaining polarized images;   reducing glare in the polarized images to form enhanced contrast images;   detecting persons or objects behind the surface from the enhanced contrast images.   
     
     
         2 . The method of  claim 1 , where the object is a human and the surface is the windshield or window of an automobile. 
     
     
         3 . The method of  claim 1 , further comprising displaying the enhanced contrast images to a user. 
     
     
         4 . The method of  claim 1 , further comprising annunciating a detected person to a user. 
     
     
         5 . The method of  claim 1 , using a human face detected as input to a facial recognition system. 
     
     
         6 . The method of  claim 1 , further comprising mounting the polarimeter on a pole or in a car. 
     
     
         7 . The method of  claim 1 , wherein the polarimeter is handheld and operated by a user from a side of a road. 
     
     
         8 . The method of  claim 1 , further comprising employing an external source of illumination. 
     
     
         9 . The method of  claim 8 , wherein a polarization state of the external illumination is optimized to further reduce glare. 
     
     
         10 . The method of  claim 1 , wherein the surface is water. 
     
     
         11 . The method of  claim 1 , wherein the step of reducing glare in the polarized images to form enhanced contrast images comprises selecting an optimal pixel from within a super pixel of polarizing filters and displaying the optimal pixels. 
     
     
         12 . The method of  claim 11 , wherein the step of selecting an optimal pixel from within a super pixel of polarizing filters comprises determining which individual pixel within the super pixel has the lowest value, and selecting that pixel value for display. 
     
     
         13 . The method of  claim 12 , wherein the step of selecting an optimal pixel from within a super pixel of polarizing filters further comprises repeating, for every super pixel in a region of interest, the steps of selecting an optimal pixel from within a super pixel of polarizing filters, determining which individual pixel within the super pixel has the lowest value, and selecting that pixel value for display. 
     
     
         14 . The method of  claim 11 , where a super pixel comprises four pixels, the four pixels polarized at 0, 45, 90, and 135 degrees, respectively. 
     
     
         15 . The method of  claim 11 , where the pixels in the pixelated polarizer array are oriented at −20, −10, 0, 10, and 20 degrees. 
     
     
         16 . The method of  claim 1 , wherein the step of reducing glare in the polarized images to form enhanced contrast images comprises computing an image comprising a weighted sum of reported intensities from a super-pixel that minimizes glare,
 reducing glare in the polarized images.   
     
     
         17 . The method of  claim 16 , further comprising determining the optimal angle of polarization to reduce glare as the angle orthogonal to the angle of polarization reported for each pixel of the polarimeter. 
     
     
         18 . The method of  claim 16 , wherein a rotating retarder is placed in front of the PPA and rotated to optimally minimize glare. 
     
     
         19 . The method of  claim 18 , wherein the rotating retarder is dynamically positioned.